An effective means of achieving a portable, ultrafast blue-light source using a variety of nonlinear media is demonstrated. We investigate the relative merits of aperiodically-poled bulk and waveguide nonlinear crystals in comparison to periodically-poled structures.

We demonstrate an effective means of achieving compact, truly portable, and entirely self-contained ultrafast blue light sources. Using a variety of nonlinear media to achieve simple second-harmonic generation of a femtosecond Cr:LiSAF laser, we investigate the relative merits of aperiodically poled bulk and waveguide nonlinear crystals in comparison to periodically poled structures. Such a compact and convenient source of ultrashort laser pulses in the blue spectral region could be of great interest for on-site applications spanning a host of disciplines, such as biomedical imaging, optical micromanipulation, and high-resolution spectroscopy.

The present invention concerns a coherent light source based on frequency conversion of the radiation from two lasers (20, 21) by frequency mixing in optical waveguides (10; 90), which are provided in a substrate (1). The wavelengths for the two lasers (20, 21) should be such, that the phase matching condition for the optically nonlinear frequency conversion is fulfilled in the waveguide structure (10; 90). The frequency conversion is accomplished in the form of frequency mixing, frequency doubling or down conversion in frequency by parametric oscillation so that in total three or four new wavelengths can be generated. By using integrated optics technique the output radiation can be controlled in various ways, for example be switched to different output waveguides, varied in intensity or colour balance.

A waveguide (and a method for fabrication of a waveguide) for electromagnetic waves, arranged in an optically non-linear crystal substrate (1), such as LiNbO3, LiTaO3 or KTiOPO4, whereby a periodically domain-inverted structure, with periodically reversed ferroelectric polarity, is provided in a channel waveguide (6), having a higher refractive index than other parts of the substrate. The regions of reversed ferroelectric polarity are achieved by means of a heat treatment yielding a domain-inversion governed by a periodic perturbation in the crystal surface, obtained by use of a periodic mask structure on the crystal surface. The periodic structure is arranged in such a way that it constitutes a quasi-phase-matching structure. Thereby the waveguide is capable of converting light or radiation of a certain wavelength (certain wavelengths) to light or radiation of another predetermined wavelength (other predetermined wavelengths) with high efficiency.

We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer ( polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.

Segmented waveguides for wavelength conversion (e.g., waveguides comprising alternating sections of crystalline substrate having the formula K1-x Rbx TiOMO4 where x is from 0 to 1 and M is P or As and sections of substrate material in which cations of said substrate have been partially replaced) and devices and processes employing segmented waveguides for wavelength conversion are disclosed wherein a periodic structure along the waveguide provides a Bragg reflection having a wavelength essentially equal to the wavelength of the input wave used for wavelength conversion. Also disclosed is a process for preparing a channel waveguide for a wavelength conversion system wherein areas along a portion of a crystal substrate surface used for forming the desired channel are alternately masked and unmasked during cation replacement by immersion in a molten salt.

We present theoretical and experimental investigations on ground-state direct pumping at 869 nm into the emitting level F-4(3/2) of end-pumped quasi-three-level Nd:YAG lasers operating at 946 nm. We have demonstrated, what we believe is for the first time, a Nd:YAG laser at 946 nm directly pumped by diodes and obtained 1.6 W of output power.

Reflection second-harmonic generation from the polished waveguide end face was used to investigate the nonlinear properties of LiNbO3-implanted waveguides fabricated by use of 2-MeV He+ and 1.5-Mev H+ beams. Results were compared with waveguides obtained by protonic exchange in benzoic acid, In contrast to the exchanged sample where the nonlinearity is strongly reduced, the implanted samples showed that the guiding region presents rather the same response as the substrate. The area where the optical barrier is located showed a strongly enhanced second-harmonic signal that was likely to be due to structural modifications in this area. Moreover, the investigation of the annealing effect showed strong interaction of protons with the lattice compared with that of He+ ions.

The second-harmonic conversion efficiency within the PPKTP waveguide is investigated using two separate tunable CW Ti:sapphire lasers at 800 nm and 980 nm. Results show strong conversion efficiency which imply that the local damage-induced index modification does not adversely affect the periodic domain structure in the material.

Frequency doubling is demonstrated in femtosecond-laser-created single-mode waveguides written in a periodically-poled potassium titanyl phosphate crystal. Conversion efficiencies of 0.22%/W (0.02%/W) were obtained for first (third) order phasematching at 980nm (800nm).

Frequency doubling has been achieved in femtosecond-laser-inscribed single-mode waveguides written in two periodically-poled potassium titanyl phosphate crystals. A conversion efficiency of 0.22 %W-1 was obtained for first-order quasi-phase matching at 980 nm and an efficiency of 0.02 %W-1 for third-order quasi-phase matching at 800 nm.

A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.

A nonlinear photonic crystal with a rectangular domain lattice of 6.09x6 mu m(2) has been fabricated and characterized in flux-grown KTiOPO4. It was used to demonstrate continuous-wave and multiple beam tunable blue second harmonic generation.

We report on fabrication and characterization of a nonlinear photonic crystal with a rectangular lattice in a KTiOPO4 crystal. The structure was used to demonstrate CW tunable second harmonic generation in the blue regime.

A submicron domain grating has been created in a bulk ferroelectric. Electron-beam lithography and electric-field poling were used to fabricate the 800 nm period grating in a 0.5-mm-thick flux-grown KTiOPO4 sample. The domain structure was characterized with an atomic force microscope and was used to demonstrate electrically amplitude adjustable Bragg reflections.

1mm thick KTiOPO4 was poled with 720nm domain period by employing UVlithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.

1mm thick KTiOPO4 was poled with 720nm domain period by employing UV-lithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.

A 1 turn thick flux-grown KTiOPO4 sample was poled with a 720 nm domain period by employing deep-UV laser lithography, chemical patterning, and electric field poling. An atomic force microscope was used to characterize the periodic domain structure. The sample was used to demonstrate sixth and seventh order quasi-phase-matched backward second-harmonic generation.

The inverse piezoelectric effect is used to produce high-resolution images of ferroelectric domains in periodically poled KTiOPO4 crystals on their nonpolar y-face using atomic force microscopy. We demonstrate that the technique is convenient for studying the nucleation and growth of domains in a periodically poled KTiOPO4 sample.

Some novel techniques to do periodic poling of KTP are described. Emphasis on ways to avoid domain broadening and merging of domains is presented with reference to the original properties of flux grown KTP. For sub-Am structures E-beam lithography and deep UV-laser lithography were used to pattern the samples, and chemical process to promote selective poling to obtain high quality domain gratings in up to 1 mm thick samples.

The fast dynamic evolution of ferroelectric domains during electric field poling in flux grown KTiOPO4 crystals was investigated online by a digital holography based technique. The dependence of the ferroelectric domain kinetics on the electric field temporal wave form and poling history was studied. High-speed imaging by means of a complementary metal-oxide-semiconductor image sensor camera allowed in situ measurement of the domain wall propagation speed under different poling conditions. The results also give evidence of the strong influence of the dielectric surface layer in this material.

The domain structure of periodically poled KTiOPO4 crystals were studied on both the polar and nonpolar faces utilizing a voltage-modulated atomic force microscope. The measurements give information of domain nucleation, growth, and merging. Two different kind of overpoling behaviors have been observed depending on the magnitude of the applied field.

We review the recent advances in fabrication of ferroelectric-domain gratings of sub-μm periodicity in KTP and Rb-doped KTP for counter-propagating second-order nonlinear optical interactions. Their performance as QPM devices will be discussed.

We present the fabrication of bulk sub-micrometer ferroelectric domain gratings in KTiOPO4 for QPM counter-propagating interactions. We demonstrate that bulk Rb-doped KTiOPO4 is a promising candidate for fine-pitch periodic poling.